The courier will deliver your order the next day or will to the neighbour. You will get a card in the mailbox with more details about the unsuccessful delivery attempt. You can also use this card to contact the courier service to make a new appointment for delivery.
You can also use the Track & Trace link of your order to change the delivery address or delivery date or have the package delivered to a GLS ParcelShop where you can pick it up yourself. You will receive the Track & Trace email separately from GLS after your order has been sent.